Known optical coherence tomography (OCT) instruments obtain tomographic images of objects by measuring distributions of amounts of reflection in the depth directions of objects using optical interference (for example, Patent Literature 1 and 2). The OCT instrument has been used for a biological diagnosis of, for example, an eyeball and a tooth since the OCT instrument can create an image of the internal structure of an object with high spatial resolution.
In the OCT instruments described in Patent Literature 1 and 2, light is separated into measurement light and reference light and an object to be measured is irradiated with the separated measurement light. The measurement light reflected on the object to be measured is combined with the reference light and generates interference light. This interference light is detected with a photodetector. An intensity distribution of reflection light in the depth direction of the object is measured as a one-dimensional tomographic image by analyzing the detection result. Moreover, a two-dimensional or three-dimensional tomographic image can be obtained by scanning a position to be irradiated, in the object, with the measurement light.